The dynamic process of formation of protein assemblies is essential to form highly ordered structures in biological systems. Advances in structural and synthetic biology have led to the construction of artificial protein assemblies. However, development of design strategies exploiting the anisotropic shape of building blocks of protein assemblies has not yet been achieved. Here, the 2D assembly pattern of protein needles (PNs) is controlled by regulating their tip‐to‐tip interactions. The PN is an anisotropic needle‐shaped protein composed of β‐helix, foldon, and His‐tag. Three different types of tip‐modified PNs are designed by deleting the His‐tag and foldon to change the protein–protein interactions. Observing their assembly by high‐speed atomic force microscopy (HS‐AFM) reveals that PN, His‐tag deleted PN, and His‐tag and foldon deleted PN form triangular lattices, the monomeric state with nematic order, and fiber assemblies, respectively, on a mica surface. Their assembly dynamics are observed by HS‐AFM and analyzed by the theoretical models. Monte Carlo (MC) simulations indicate that the mica‐PN interactions and the flexible and multipoint His‐tag interactions cooperatively guide the formation of the triangular lattice. This work is expected to provide a new strategy for constructing supramolecular protein architectures by controlling directional interactions of anisotropic shaped proteins.
Noncontact manipulation of nano/micromaterials presents a great challenge in fields ranging from biotechnology to nanotechnology. In this study we developed a new strategy for the manipulation of molecules and cells based on diffusiophoresis driven by a concentration gradient of a polymer solute. By using laser focusing in a microfluidic device, we created a sharp concentration gradient of poly(ethylene glycol) (PEG) in a solution of this polymer. Because diffusiophoresis essentially depends on solute gradients alone, PEG solute contrast resulted in trapping of DNA and eukaryotic cells with little material dependence. Furthermore, quantitative analysis revealed that the motility of migrating cells was enhanced with the PEG concentration, consistent with a theoretical model of boosted cell migration. Our results support that a solute contrast of polymer can exert an interfacial force gradient that physically propels objects and may have application for the manipulation of soft materials.
The control of solute flux by either microscopic phoresis or hydrodynamic advection is a fundamental way to transport molecules, which are ubiquitously present in nature and technology. We study the transport of large solutes such as DNA driven by a time-dependent thermal field in a polymer solution. Heat propagation of a heat spot moving back and forth gives rise to the molecular focusing of DNA with frequency-tunable control. We develop a model where the viscoelastic expansion of a solution and the viscosity gradient of a smaller solute are coupled, which explains the underlying hydrodynamic focusing. This effect offers novel non-invasive manipulation of soft and biological materials in a frequency-tunable manner.
Transport of ions and molecules under external field gradients is fundamental phenomena relevant to many biological systems including molecular motors in nature. As inspired from such biological transport, novel optical manipulation by using local solute gradient and the creation of self-propulsive particles are being developed using this technology. In this review article, we describe the basic principles behind those transport phenomena under a temperature and a solute concentration gradient and discuss novel manipulation tools for soft biological materials. The control of such micron-scale transport will bring new insight in design principles of functional materials showing autonomous motion as seen in molecular motors.
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